In a telephone conference system, it is desirable to provide each conference participant or subscriber with the sum of all the signals in the conference excluding his/her own. One technique for accomplishing this result is to apply all signals to a multi-port bridge network, which is so structured that the signals at each port are prevented from returning to the corresponding port. This technique is limited in the number of signals that can be combined in conference before great complexity sets in, as shown in U.S. Pat. No. 1,944,283. Another technique involves sampling the various inputs, storing them, and then switching all but the appropriate input signals to the corresponding output. Such a system is shown in U.S. Pat. No. 3,924,082. In a further technique all the inputs are summed and returned to all the outputs where a corresponding input signal is subtracted from the summed signal. Such a system is shown in U.S. Pat. No. 3,399,275.